1. Field of the Invention
This invention relates to a photocurable and thermosetting composition which is possessed of heat resistance and suitable as a solder resist ink for the direct drawing by means of an ink jet printer and to a printed circuit board having a solder resist pattern directly drawn thereon by the use of the composition.
2. Description of the Prior Art
As a method for the manufacture of printed circuit boards using an ink jet printer, a method which comprises forming an etching resist by drawing a conductor circuit pattern on a metal foil laminated on a plastic substrate by means of an ink jet printer and performing an etching treatment has already been proposed (see Published Japanese Patent Applications JP 56-66089 A, JP 56-157089 A, JP 58-50794 A, and JP 6-237063 A). Since this method performs the direct drawing according to CAD data, it has such advantages that the time and labor required for the process may be considerably reduced and, at the same time, such expendables as a developing solution, a resist ink, and a washing solvent may also be curtailed as compared with the patterning by a photolithographic developing process which requires a photo-mask and uses a photosensitive resin and a method for performing the patterning with a resist ink by a screen printing process.
Also as to a solder resist which protects a conductor circuit formed on a printed circuit board, the formation thereof by means of an ink jet method has already been proposed (see JP 7-263845 A and JP 9-18115 A) and the method is the same as that for an etching resist. In this case too, the number of steps, time, and expendables may be reducible as compared with the photolithographic developing method or the screen printing method. Furthermore, the division of an ink tank to those for an etching resist, a solder resist, a marking ink, and the curing agents thereof and the sharing of a printer therefor for the purpose of further making use of the advantages of the ink jet system has also been proposed (see JP 8-236902 A).
However, the ink for the ink jet system is subjected to such restriction that its viscosity should be not more than about 20 mPa·s at the time of application thereof. This viscosity is far different from the viscosity of the ink to be used in screen printing, around 20,000 mPa·s, and even if this ink is diluted with a large amount of diluent, it will be difficult to lower its viscosity to a desired level. Moreover, even if the decrease in viscosity is attained, conversely the physical properties required of a solder resist, such as heat resistance and resistance to chemicals, will deteriorate considerably. Furthermore, when it is diluted with a volatile solvent, a nonvolatile content becomes very low and, as a result, it will be difficult to attain a sufficient film thickness. Therefore, the above-mentioned ink jet system remains at an idea level as far as a solder resist of a printed circuit board is concerned, and the practical solder resist ink which can be used with an ink jet printer did not exist.